Mold release agents, as reported in "The Mold Release Quandary", Plastics Technology, pages 65-70 September, 1980, must form a film or vapor interlayer on the mold tool surface. This layer should be inert to the molding material and not attack the tool surface. At the end of each molding cycle, the release agent should also enable an easy release of the molded part such that the part has no surface attack or visible surface defect, in other words, a "Class A Surface". When used for the release of HR foamed plastics where the surface of the molded parts has open cells and closed cells, the mold release agent employed should leave the open cells free; that is, should not block the opens cells since this would adversely affect or lower the desired high resilience of the molded foam part. A release agent generally contains a blend of several ingredients including active ingredients which cause the release action, a solvent, a film-former, a drying or curing agent, and added lubricant to enhance releasability. Ingredients can range from greases, natural waxes, soaps, emulsions, mineral oils, fats, lecithins, metal stearates, silicones, fluorocarbons, synthetic waxes, organophosphates, polyaliphatic alcohols and polymeric resins. There are several key criteria (other than those mentioned) for selecting a particular mold release agent such as ability to clean the release agent from the mold, compatibility of the release agent (if carried away on the part surface or if allowed to build-up on the mold surface), health and safety risks of exposure to flammable or toxic ingredients of the release agent, and relative cost both of the release agent and its use. Ideally, the release agent when coated as a layer onto the tool surface should not be too soft so that it is removed or "scrubbed" each time the resin is injected into the mold. In other words, it should be sufficiently hard that it remains intact (i.e., does not flake-off or transfer to the part) as a suitable release layer for a number of injection and release cycles, without requiring replacement. Also, the release layer once established should remain sufficiently protective that the resin or foam does not "strike through" and build-up unreleasably on the tool surface. Further, it should not retain water. For example, in the case of isocyanate-reacting foams, water causes the formation of polyurea which is an undesirable part surface contaminant that causes problems with later steps of processing the part. It has been proposed to use a high molecular weight saturated or unsaturated fatty acid soap such as the oleate or the isostearate as a release agent for molding. The difficulty with use of an oleate or isostearate release agent, however, is that each is associated with part surface attack, water retention, polyurea build-up and/or foam build-up. Also, while the higher fatty acid soaps such as sodium soaps or potassium soaps may be satisfactory as a release agent where the molded part surface is a closed-cell foam surface, they are not satisfactory for applications in high resiliciency foams where the surface of the molded part is required to be an open-cell surface so that there is as little restriction of gas flow through its structure as possible during deformation and stress recovery (cf. Advances in Urethane Science and Technology, Vol. 3, 108, Technomic Publishing, Inc., Westport, Conn., 1973).
It is therefore an object of the present invention to provide novel mold release agents and means of application which agents are applied as a durable yet readily cleanable protective release layer or coating on mold surfaces for purposes of plastic molding.
It is also an object of the invention to provide mold release agents for polyurethane molding which, in coated form for the molding and release of parts, perform efficiently without substantial scrubbing, flaking, part surface attack, water retention, polyurea build-up, strike-through or foam build-up.
It is a further object to provide mold release agents and means for their application which do not involve use of an objectionable organic solvent in an industrial environment.
It is still another object to provide mold release agents which are economical, provide an open-cell surface on the molded parts, and are disposable at low cost by ordinary waste disposal methods.
These and other objects, features and advantages will be seen from the following detailed description of the invention.